In order to increase the production of a thermoforming machine, it has been a common practice in the plastic industry to use two molds mounted side by side and to alternately move these molds under a forming die assembly and then under a part-retrieving station. The parts formed in the first mold are retrieved from this mold while other parts are being formed in the other mold, and vice versa. These machines are characterized by the similarity of their mold-supporting tables mounted on rails and linear bearings for horizontal movement of the molds from side to side.
Examples of dual-mold thermoforming machines of the prior art are described in the following US patents.
    U.S. Pat. No. 4,105,736 issued Aug. 8, 1978 to Pietro Padovani;    U.S. Pat. No. 5,304,050 issued Apr. 19, 1994 to Mario Vismara; and    U.S. Pat. No. 5,453,237 issued Sep. 26, 1995 to Pietro Padovani.
The mating of a mold with a forming and cutting die during a thermoforming process must be done with great precision to ensure an uniform wall thickness of the molded parts and a proper severing of the molded parts from a plastic sheet. Such precision requires that the molds and the mold-supporting tables be inflexible. The magnitude of the forces generated during the forming and cutting phases also requires that the molds and the mold-supporting tables have robust structures. As it is known, machine stiffness and strength are often associated with high mass, and high mass hinders acceleration, deceleration and cycle speed.
The thermoforming machines of the prior art are known to consume great amounts of energy to accelerate their mold-supporting tables from one molding position, and to dissipate equally large amounts of energy to decelerate the tables at the other molding position. Because of this energy constraint, basically, the cycle speed of the dual-mold thermoforming machines of the prior art has been limited by the capacity of these machines to move heavy molds quickly and precisely.
Therefore, it is believed that a need still exists in the industry for a better dual-mold thermoforming press which is less affected by the inertia of its molds and mold-supporting table.